Innate Immunity

What is innate immunity

A rapid, non-specific immune defense that recognizes conserved pathogen features and does not form long-term memory

What is the humoral response of innate immunity

The complement system, which uses blood-borne enzymes to attack pathogens.

How does complement directly kill pathogens

By forming membrane pores that lyse foreign cells and disrupt their functions.

What is phagocytosis

The engulfment and digestion of pathogens by immune cells.

What are cytokines and chemokines?

Signaling molecules that recruit and activate immune cells during inflammation.

What is adaptive immunity

A specific immune response that develops after antigen exposure and forms immune memory.

What is the humoral response of adaptive immunity

Antibodies produced by B cells that bind and neutralize pathogens.

What is the cell-mediated response of adaptive immunity

T cells kill pathogen-infected host cells and generate memory T cells.

What is the complement system?

A network of ~35 soluble and cell-surface proteins that enhance pathogen elimination.

What are the three complement activation pathways?

Classical, lectin and alternative pathways

What activates the classical complement pathway?

Antibody-bound pathogens.

What activates the lectin complement pathway

Mannose-binding lectin binding sugars on microbial surfaces.

What activates the alternative complement pathway

Spontaneous activation on pathogen surfaces

What molecule is the central control point of complement?

C3

What are the products of C3 cleavage

C3a, which promotes inflammation, and C3b, which mediates opsonization and amplification.

What is the membrane attack complex (MAC)?

A pore-forming complex that lyses pathogen membranes.

What are PAMPs

Conserved molecular patterns found on pathogens but not host cells.

What are PRRs

Host-encoded receptors that detect PAMPs and activate innate immunity.

What happens when PRRs bind PAMPs

Immune signaling pathways trigger inflammation, chemotaxis, and gene expression changes

What are Toll-like receptors (TLRs)

Transmembrane PRRs located on the cell surface or endosomal membranes.

Why are some TLRs located in endosomes

To detect pathogen nucleic acids after endocytosis.

Why are CpG sequences immunostimulatory

They are unmethylated in bacteria and viruses but methylated in host DNA

What is lipopolysaccharide (LPS)

A Gram-negative bacterial outer membrane component that acts as an endotoxin.

What are the three components of LPS

O-antigen, core oligosaccharide, and lipid A.

What is lipoteichoic acid (LTA)

polymer in Gram-positive bacterial cell walls anchored to the membrane.

What are NOD1 and NOD2?

Cytosolic PRRs that detect bacterial peptidoglycan fragments.

What ligand does NOD2 recognize?

Muramyl dipeptide (MDP).